HOLE : SOME INDIAN GRASSES AND THEIR CECOLOGY. J*7 



slightly increases, owing to a small admixture of clayey particles, or organic humus, 

 Saccharum Munja becomes the dominant species. While intermediates between these two 

 communities thus occur, there is a marked dominance of Aristida on the very dry coarse- 

 grained soil and of Saccharum on the relatively moist and fine-grained soil. Similarly in 

 the Saccharum Munja savannah, in places where the soil is distinctly wet, usually on 

 account of a considerable increase in the proportion of clay, Erianthus appears and 

 gradually connects the moist with the wet savannah. Erianthus, while approaching swamp 

 very closely, does not itself actually enter into the typical swamp community found on 

 perennially water-logged soil, but Saccharum spontaneum var. nepalense and Imyerata 

 arundinacea var. latifolia both find a congenial habitat in the soft, spongy, perennially 

 thoroughly saturated soil of the marsh; other forms of both these species are found in the 

 moist savannah, and Saccharum spontaneum also occurs in the steppe. 



The Saccharum Narenga savannah is usually a very well marked type, but here also 

 small areas may occasionally be found where this species occurs in company with Saccharum 

 Munja and also with Erianthus Ravennm. Such an admixture is usually brought about 

 in nature as the result of a regressive change in the soil. When sal forest on light loamy 

 soil, for instance, is felled, provided the area is sufficiently large, the proportion of humus, 

 and consequently the capacity of the soil for retaining water, rapidly decreases, while the 

 soil also becomes dried by exposure to the sun and air currents. In such conditions 

 Saccharum Munja and Saccharum Napenga may be found together, the former eventually 

 becoming dominant and ousting the latter, if frost or other factors prevent the re-establish- 

 ment of woodland. 



Similarly if moist, mixed forest on heavy soil (especially if it contains a considerable 

 admixture of Sal) is felled, the resulting decrease in humus content tends to make the soil 

 denser and thus less porous, while the rapid movement of water by capillary action is 

 checked. The soil thus tends to become less aerated and more liable to become somewhat 

 water-logged during the rainy season. 



In such conditions both Saccharum Narenga, and Erianthus Ravennce may coexist for 

 a time and these species may thus be found together. If the cleared area is extensive, 

 however, the drying action of sun and wind soon makes the habitat too dry for Erianthus 

 and it may be replaced by the moist savannah form of Imyerata and Saccharum spontaneum 

 and by less strongly mesophilous species of Andropogon and Pollinia. 



In dealing with this question of intermediate forms, also, it must be remembered that, 

 in addition to the very gradual changes in the intensity of the factors of the locality, we 

 must allow for the undoubted fact that the constitution and adaptations of a particular 

 species frequently enable it to thrive in essentially different habitats and to enter into the 

 constitution of essentially different communities. Thus Saccharum spontaneum enters 

 into the composition of the steppe — Aristida community, it forms a part of a typical reed- 

 swamp community, and finally may be often found in mesophilous grasslands. 



Similarly Imperata arundinacea is found locally in both moist and wet savannah, 

 usually on heavy clay, which is liable to become water-logged during rain and to become 



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